1. Field of the Invention
The present invention relates to a high quality silicon (Si) single crystal ingot having desirable oxygen concentration, and more particularly, a high quality Si single crystal ingot and wafer and a growth method and apparatus thereof, in which the temperature distribution and the oxygen concentration distribution of Si melt are controlled independently from each other during the growth of an Si single crystal ingot by the Czochralski method in order to produce a high quality Si single crystal ingot and wafers which have controlled growth defects and oxygen concentrations desirable to customers.
2. Description of the Prior Art
As well known in the art, in order to grow a high quality silicon (Si) single crystal ingot that can enhance the yield of semiconductor devices, temperature control has mainly been conducted on high temperature distribution of the single crystal ingot after crystallization. This is done in order to control contraction-induced stress and so on, resulting from cooling subsequent to crystallization or behavior of point defects built up in solidification.
Also, in order to meet various oxygen specifications (suitable for semiconductor devices) demanded by customers, additional capital has been invested. For example, process parameters such as pressure and argon (Ar) flow rate are adjusted, hot zones are changed, and horizontal strong magnetic field is introduced.
According to a typical process of the Czochralski growth of Si single crystal, polycrystalline Si is loaded into a quartz crucible where it is melted into Si melt under the heat radiated from a heater, and then a Si single crystal ingot is grown from the surface of Si melt. When growing the Si single crystal ingot, the crucible is elevated through the rotation of a shaft that supports the crucible, maintaining the solid-liquid interface at a constant level, and the Si single crystal ingot is wound up while being rotated coaxially with the crucible but with an opposite rotating direction. Upon being grown as above, the Si single crystal ingot is produced into Si single crystal wafers (via wafer machining such as slicing, lapping, polishing and cleaning), which are in turn used as semiconductor device substrates.
In addition, as a typical technique for promoting the growth of the Si single crystal ingot, an inert gas such as Ar is introduced to an ingot-growing apparatus via an upper part thereof and then exhausted from the ingot-growing apparatus via a lower portion thereof.
In addition, for the purpose of stable single crystal ingot production and effective oxygen concentration adjustment, a magnetic field such as a CUSP magnetic field, vertical magnetic field and horizontal magnetic field is generally used with at least a predetermined strength.
Conventional techniques for growing a Si single crystal ingot as above have used a heat shield in order to regulate the temperature gradient of a growing Si single crystal and oxygen evaporation from Si melt. Examples of such conventional techniques may include Korean Patent No. 374703, Korean Patent Application No. 2000-0071000 and U.S. Pat. No. 6,527,859 and so on. As, according to a report by Machita et al., “The effects of argon gas flow rate and furnace pressure on oxygen concentration in Czochralski-grown Si crystals” (Journal of Crystal Growth, 186 (1998) 362-368), and Korean Patent Application No. 2001-7011548, installation of a hot zone such as a gas flow controller as well as adjustment of pressure, Ar flow rate and rotation speed of a crucible are proposed as means for controlling oxygen concentration. Furthermore, Japanese Laid-Open Patent Application Nos. 2000-247788 and H10-130100 disclose restraining oxygen dissolution and melt convection by using an apparatus for adjusting magnetic field strength and a unit for generating a multi-CUSP magnetic field.
However, adjustment of several process parameters of the prior art cannot efficiently control the temperature gradient or oxygen concentration of a Si single crystal ingot. So, it has been impossible to produce a high quality Si single crystal ingot and wafer with low point defect concentration that have oxygen concentrations desirable to customers.
Conditions for preferable wafer substrates suitable for device process are as follows: In an active device region formed from a wafer surface to several microlayers in depth, it is preferable to eliminate all agglomerated defects such as vacancy and self-interstitial, except for point defects. For example, Crystal Originated Pit (COP), as a type of point defects with agglomerated vacancies worsens Gate Oxide Integrity (GOI), thereby dropping device's yield. Furthermore, GOI may worsen if micro precipitates depending on oxygen and vacancy concentration have occurred in the active device region. On the other hand, Bulk Micro Defect(BMD) containing micro precipitates is needed in a bulk region deeper than the active device region. The MBD occurring during heat treatment of a semiconductor device is harmful for the active device area, but improves device's yield by gettering of metal impurities existing in the wafer surface and the active device region. Therefore, a preferable wafer substrate needs suitable vacancy and oxygen concentration.
Meanwhile, as described in Korean Patent Application Nos. 1999-7009261, 1999-7009307 and 1999-7009309, the prior art expresses vertical temperature gradient of crystal in the form of G0=c+ax2. So, vacancy concentration increases gradually to the center from the outer circumference of a single crystal ingot but interstitial concentration decreases. If out-diffusion does not take place by a sufficient degree around the outer circumference of the single crystal ingot, an interstitial crystal defect such as LDP occurs. This causes crystal growth to be carried out with high vacancy concentration in the center. Therefore, a vacancy crystal defect (e.g., void, Oxidation induced Stacking Fault (OiSF)) tends to occur in the center of a wafer owing to vacancy concentration much higher than balance concentration. On the other hand, dropping the cooling rate of crystal for the purpose of interstitial out-diffusion further requires installation of additional hot zones. This decreases the growth rate of the single crystal ingot, thereby lowering productivity.
As approaches for controlling the temperature distribution of a Si single crystal ingot in order to produce a high quality Si single crystal ingot, following conventional technologies have been proposed. Japanese Patent Application No. H02-119891 proposes to control temperature distribution in the center and circumference of a Si single crystal ingot by adopting hot zones during cooling of the ingot in order to reduce crystal defects in the ingot owing to the strain of solidification. This document particularly discloses using a cooling sleeve to increase solidification rate in the growth direction of the single crystal ingot and thus decreasing lattice defect. Furthermore, Japanese Patent Application No. H07-158458 proposes to control the temperature distribution and pulling rate of a single crystal ingot. Japanese Patent Application No. H07-066074 proposes to improve a hot zone and control cooling rate in order to restrain crystal defect formation by using point defect diffusion. Korean Patent Application No. 2002-0021524 claims that the yield of a high quality single crystal ingot was enhanced by improving a heat shield and a water cooling pipe. Japanese Patent Application H05-061924 proposes to impart periodic variation to the growth rate of a Si single crystal ingot in order to prevent a crystal defect in the single crystal ingot by using the hysteresis of a region where a crystal defect such as OSF and oxygen precipitation defect takes place.
Conventional techniques for controlling the oxygen concentration of a Si single crystal ingot include Japanese Laid-Open Patent Application No. 10-013010, Korean Patent Registration No. 10-0239864, Korean Patent Application No. 2001-7011548 and so on. However, these techniques have drawbacks in that either they require additional investment or the high quality single crystal is not actually produced.
Furthermore, Korean Patent Registration No. 10-0271504 discloses a technique for locating the center of a CUSP magnetic field at a position of at least ⅓ depth of the total depth of Si melt in order to remove a slit formed in the growth direction and thus improve oxygen distribution in the radial direction. Korean Patent Registration No. 10-0239864 discloses a technique for ensuring uniform magnetic field distribution by using a superconductive horizontal magnetic field in order to restrain convection. Korean Patent Application Publication No. 2002-0081470 discloses a technique for adjusting the relation between solid-liquid interface configuration and crystallization temperature. However, such conventional techniques have not disclosed using an unbalanced magnetic field in order to control oxygen concentration in a high quality Si single crystal ingot that is free of agglomerated crystal defects.
Moreover, according to the afore-mentioned techniques, the sought-after high quality single crystal ingot can be produced only with a low yield.